at first homogenize liver tissue on TES lysis bufferthen take 100 ul of the homogenate to new eppendorf adding 50 ul proteinase k - incubate at 37 C with shaking overnightthen load sample onto the gel

Than, this is the correct image of your DNA. You see a smear when you treat this way. If you use DNase or you sonicate, you will see some bands...

Using DNase or RNase??sonication will affect the fragmentation?????????????????/

Well, when you sonicate you shear the DNA and you areable to see distinct bands. If you do not sonicate, you usually see a lot of DNA in the well and a smear. Using micrococcus DNase will have the same effect of sonication.As for "normal" images of DNA you can have a look here: www.biomedcentral.com/1471-2202/6/13/figure/F2